This invention relates to an improved rotary tool adapted for grinding under a flowing liquid film wherein the particles of abrasive are metal-bonded to a rigid supporting surface.
In the wet grinding of hard materials such as amethyst and sapphire with metal-bonded abrasive, e. g., diamond particles, it is known that a limiting factor governing the cutting rate is the accumulation and packing of detritus at the roots of the particles of abrasive, filling the intergranular spaces and ultimately burying the abrasive grains. For all practical purposes the cutting action ceases when the abrasive grains are buried in the detritus.
To improve the removal or scavenging of the detritus from the intergranular interstices it was taught, e.g., by G. F. Keeleric in U.S. Pat. No. 2,820,746 issued Jan. 21, 1958, to cluster the abrasive into tiny dots less than 1/4 inch in diameter leaving a major portion of the area unoccupied by abrasive. The density of population of abrasive particles per total working area of the tool was thereby reduced significantly. With this configuration the initial cutting rate was substantially increased. However, under hard grinding conditions, e.g., with a sapphire workpiece, the cutting rate dropped to about half of the initial rate within a relatively short service period.
One of the objects of the invention is to prolong the service life of the grinding tool.
Another object of the invention is to provide more abrasive particles per total area of the tool without necessarily increasing the local density of packing of abrasive particles within the working clusters or elements.
Another object of the invention is to improve the scavenging of detritus from the roots of the particles of abrasive.
Another object of the invention is to improve the quality of grinding and thereby to reduce the conventional number of grinding steps with progressively finer abrasive tools in the sequence prior to final polishing.